The present invention relates to an arrangement for extracting divergence-measuring modes from a corrugated guide. It also relates to the application of such an arrangement to a tracking antenna.
By a corrugated guide is meant a guide, generally of circular cross-section, which contains transverse grooves whose depth is of the order of a quarter of the operating wavelength and which are spaced apart by a fraction of this wavelength.
In my copending application Ser. No. 533,722, now U.S. Pat. No. 3,964,070, I have described means for extracting divergence-measuring modes from a corrugated horn. In that prior patent I have pointed out the benefit of using corrugated horns in tracking antennas, such horns having radiation diagrams which are almost figures of revolution with low sidelobes, and having stable amplitude and phase characteristics over frequency ranges of little less than an octave. These useful properties of corrugated horns are also made use of in a system according to my present invention, in which the divergence-measuring modes are extracted from a corrugated guide connected to the horn.
In fact, in the context of the invention the divergence-measuring modes have to be extracted in an area where the phase velocity of the useful modes is substantially constant, which is not the case in a horn where the phase velocity varies continuously along the wall of the horn, thus making it more difficult to use the differing phase velocities of the useful modes as a criterion to select the those modes.